#include <iostream>
#include <fstream>
#include <vector>
#include <bitset>
#define NMAX 2000005
#define LL long long
using namespace std;
ofstream fout("ciur.out");
ifstream fin("ciur.in");
vector <int> pr;
bitset <NMAX> isprime;

void ciur()
{
    for(LL i=2;i<=NMAX;i++){
        if(isprime[i]==0){
            for(LL j=i*i;j<=NMAX;j=j+i){
                isprime[j]=1;
            }
            pr.push_back(i);
        }
    }
}
int N,c;
int main()
{
    fin>>N;
    ciur();
    for(LL i=0;pr[i]<=N;i++){
        c++;
    }
    fout<<c;

    return 0;
}